I regularly receive questions concerning readers buying new computers. They will usually ask what antivirus software they should install to keep everything protected. I usually suggest one or two good antivirus applications. Keep in mind I am only referencing Windows machines and, due to my frugal nature, free applications.
If you have a Windows 7 system, I recommend going to Microsoft.com and searching for "Microsoft Security Essentials." Go to the download page, download it and install it. It may already be on your new computer if the manufacturer made a deal with MS to preinstall it. However, do not worry if it is, it will harm nothing to reinstall.
For a Windows 8.1 (or 8 if you have not upgraded yet…which you should ASAP) you have "Windows Defender" already installed on your computer. It comes automatically with all versions of W8. It is an upgraded version of "Security Essentials" for W8. These are both good antivirus apps and really all you need unless you go to disreputable places that may possibly be able to defeat them. They are good in that they will be updated with Windows Update so you do not have to do anything additional to get them updated as you do with all other third party apps.
Some people do not trust MS and want another antivirus software so I recommend, "Avast!" If you choose to install Avast go to, "avast.com" only. The reason is, if you search for it online you may be directed to a disreputable site. It may be listed as a free download but you may be getting something that could harm your system.
One other major application I would install on all computers today is Malwarebytes (download the free version at malwarebytes.org). I mentioned it toward the end of last year but many people have asked about it, so I feel I need to remind you.
I personally had not installed Malwarebytes on my computer figuring my antivirus software took care of everything. A year or more ago I noticed my system running slower than it should be and I found a toolbar installed on Internet Explorer I had not installed. I had not noticed it before since I do not regularly use MSIE as my browser so I had no idea how long it was on my computer. Anytime you have a toolbar on your browser that you know nothing about is not a good sign. It most likely means that you have some malware running and you need to remove it…now! So I knew my computer had been had.
Malware is software inserted when you download something, either intentionally or not, that is designed to do damage or some sort to your system. It can totally or partially disable your computer.
The first time you run Malwarebytes you may get tens to hundreds of files recognized. Delete them all! I would encourage you to run it on some sort of regular schedule. A weekly, monthly or quarterly time frame is good depending on how much you are online.
I almost guarantee if you install and run this on your old computer you will find many malware items present.